The RGRK method [1]}. Given an initial vector \(^{(0)} \in ^{n}\)  and a relaxation parameter \(\theta _1\) , for \(k=0,1,2,\cdots \) , until the iteration sequence \(\left\lbrace ^{(k )}\right\rbrace _{k=0}^{\infty }\)  converges,
we first construct the index set \(U_k\)  according to formula (REF ) and then update \(^{(k+1)}\)  in accordance with
\(^{(k+1)} = ^{(k)} + \frac{b_{i_k} - _{i_k}^T ^{(k)}}{{_{i_k}}}_{i_k},\) 
